Roller Brake Test | Your Guide to Vehicle Braking Assessment

Understanding HGV Roller Brake Testing (RBT)

An HGV roller brake test (RBT) is a controlled and safe method used to assess the braking performance of a heavy goods vehicle. This test is crucial for ensuring that the vehicle's brakes meet safety standards and operate effectively under real-world conditions. Here's a detailed breakdown of how the process works:

The Setup:

• The Roller Bed: The vehicle is driven onto a platform equipped with two sets of powered rollers under one axle at a time. These rollers are driven by electric motors and feature a textured surface to mimic real-road conditions. This setup is designed to simulate the forces a vehicle would experience during braking while maintaining a controlled environment for accurate measurements.
• Measurements and Information: Before the test begins, the tester inputs critical vehicle information into the system, including its weight, axle configuration, and other relevant details. This data is essential for calibrating the system and ensuring that the test results are accurate and applicable to the specific vehicle being tested.
• Meaningful Brake Test Setup: To conduct a "meaningful brake test," the vehicle must be loaded to simulate real operating conditions. The load applied should be at least 60% of the total axle capacity. For example, if the vehicle has a tandem axle with each axle rated at 9 tonnes (18 tonnes total for the bogie), the load imposed should be 10.8 tonnes. This ensures that the braking system is tested under conditions that closely resemble those encountered during actual vehicle operation, providing more reliable and realistic results.
• Preparing the Vehicle: Prior to testing, the vehicle undergoes a preliminary inspection. This includes checking the brakes for leaks, wear, or damage, and ensuring that tyre pressure is within the recommended range. These checks are vital for ensuring that the test results reflect the actual condition of the vehicle’s braking system without any external factors skewing the data.

The Test:

1. Roller Activation: Once the vehicle is properly positioned, the rollers are activated, spinning at a predetermined speed based on the test requirements. This speed is carefully selected to replicate the conditions under which the brakes would be used during normal driving.
2. Brake Application: The driver is instructed to apply the brakes, following specific guidelines depending on the test type. For instance, during a service brake test, the driver may be required to apply maximum braking force to assess the system’s full capability.
3. Force Measurement: As the brakes are applied, the rollers resist the rotation of the wheels, simulating the deceleration a vehicle would experience on the road. Sensors within the system measure the braking force generated by each wheel. This data point, known as the DTP (Decelerometer Test Point), is crucial for determining the effectiveness of the braking system.
4. Data Collection: The system records various parameters, including the braking force for each wheel, the overall deceleration of the vehicle, and the percentage efficiency of the braking system. These measurements provide a comprehensive view of how well the brakes are performing.

The Analysis:

1. Performance Evaluation: The collected data is analysed and compared against regulatory standards and manufacturer specifications. This evaluation helps determine whether the vehicle's braking system is performing as expected and meets the necessary safety requirements.
2. Pass Parameters for Trailers in the UK: For trailers operating in the UK, the brakes must achieve a deceleration rate of at least 45% at a pressure of 6.5 BAR to pass the roller brake test. This ensures the braking system is effective enough to safely stop the vehicle. At least one physical roller brake test is required annually. If Electronic Braking Performance Monitoring System (EBPMS) data is not available, meaningful roller brake testing should be conducted at each service to ensure ongoing compliance and safety (From April 2025 onwards, the DVSA will enforce a minimum of 4 meaningful RBTs per annum).
3. Individual Wheel Analysis: The braking force of each wheel is examined for imbalances. A significant difference in braking force between wheels can indicate potential issues such as misaligned brakes, uneven wear, or hydraulic problems. Identifying these imbalances is critical for maintaining the vehicle’s stability and control during braking.
4. Report Generation: After the test, a detailed report is generated, summarising the results. This report typically includes the braking forces measured, the overall efficiency of the braking system, and whether the vehicle passed or failed the test. This documentation is essential for both regulatory compliance and maintaining a record of the vehicle’s brake performance.

Additional Points:

• Types of Brakes Tested: HGV roller brake tests can assess different braking systems, including service brakes (primary braking system), parking brakes (used to secure the vehicle when stationary), and emergency brakes (backup system for stopping the vehicle in case of service brake failure).
• Advanced Testing Capabilities: Beyond basic performance testing, more advanced assessments can be conducted. These include evaluating brake fade (how well the brakes perform under prolonged use) and ovality testing (which checks for uneven braking due to warped brake discs or drums).
• Regulatory Importance: Regular roller brake tests are crucial for ensuring the safety of HGVs on the road. They are often a mandatory component of annual vehicle inspections and are required after any significant brake repairs. Passing these tests ensures that the vehicle is roadworthy and complies with legal safety standards.
• Exemption for Tri-Axle Trailers: Currently, tri-axle trailers are exempt from certain roller brake testing requirements in the UK. This exemption is based on the assumption that tri-axle trailers have superior braking performance due to the distribution of weight across three axles, which generally provides better stability and efficiency. However, this exemption does not mean that these trailers are free from all testing requirements. They must still meet safety standards and may be subject to other inspections or tests. It's important to note that exemptions like this are subject to review and may change as regulations evolve to ensure the highest safety standards on the road.

Conclusion:

HGV roller brake testing is an essential procedure that helps ensure the safe operation of heavy goods vehicles on the road. By accurately measuring the performance of a vehicle’s braking system, these tests help prevent accidents and maintain high standards of road safety.